The present invention relates to signal processing in a video system, and more particularly, to a high speed detector for detecting peak voltages of short duration pulses having a low duty cycle.
In a television set or the like, there is often a problem that when contrast settings are set to a high level, there is "blooming" of small areas or "white spots" on the CRT display. While the beam limiter circuits sense the brightness of large portions of display area and reduce the scanning beam of the CRT accordingly, there is a substantial time delay from when the actual initial scanning of small portions of the screen is accomplished to when the beam limiter is actuated. This delay in actuation of the beam limiter results in small portions of the display, e.g., one or two horizontal lines, or even small portions of a single horizontal line, having excess contrast luminance which will show up as a blooming effect before the beam limiter can work.
The response time of prior art peak detectors are substantially slower than what is required for the detection of short duration pulses of the type described above. Accordingly, it is desirable to detect the brightness of small portions of the CRT display, possibly down to single pixels, which are represented in the luminance signal as short duration, low duty cycle pulses, and to rapidly reduce the contrast or luminance for such small portions of the display. Accordingly, it is further desirable to provide a peak detector having a very rapid response time in order to peak detect such low duty cycle, short duration pulses.